Chapter 17: Introduction to Darwinian Evolution

Evolution Accumulation of inherited changes within populations over time NOT changes in an individual in its lifetime Changes in characteristics of populations over many generations

2 perspectives: 1) MICROEVOLUTION: short-term adaptations of population to changes in the environment 2) MACROEVOLTUION: long-term formation of different species from common ancestors

Contributing Scientists Jean Baptiste de Lamarck – 1 st – organisms undergo change because of natural phenomena – Organisms endowed with vital force to change toward complexity over time – Organisms could pass traits acquired during their lifetimes to their offspring Giraffes – stretch necks Discredited when basis for heredity discovered

Thomas Malthus – Population growth not always desirable – Outstrip food supply – Famine, disease, war – stop growth “struggle for existence” –  strong and constant check on human population growth Charles Lyell – Slow geological processes  Old Earth

Charles Darwin – HMS Beagle – South America – 5 years – Naturalist – plants, animals, fossils, geology – Galapagos Islands – compared species to mainland and other Galapagos Islands – Artificial selection: breeders develop varieties in a few generations Dogs, plants Similar process in nature – model for natural selection

Fig Kale Kohlrabi Brussels sprouts Leaves Stem Wild mustard Flowers and stems Broccoli Cauliflower Flower clusters Cabbage Terminal bud Lateral buds

Fig NORTH AMERICA EUROPE AFRICA AUSTRALIA GREAT BRITAIN SOUTH AMERICA ATLANTIC OCEAN PACIFIC OCEAN Cape of Good Hope Tierra del Fuego Cape Horn Tasmania New Zealand Andes Equator The Galápagos Islands Pinta Marchena Genovesa Santiago Daphne Islands Pinzón Fernandina Isabela San Cristobal Santa Fe Santa Cruz Florenza Española

– Favorable variations would be preserved, unfavorable eliminated –  adaptation : evolutionary modification that improves the chances of survival and reproductive success in a give environment – Accumulation of modifications  maybe new species – Time required for new species to originate Old Earth

Fig (a) Cactus-eater(c) Seed-eater (b) Insect-eater

Fig American RevolutionFrench RevolutionU.S. Civil War – The Origin of Species is published. Wallace sends his hypothesis to Darwin. Darwin begins his notebooks. Darwin writes essay on descent with modification. Darwin travels around the world on HMS Beagle. Malthus publishes “Essay on the Principle of Population.” Lyell publishes Principles of Geology. Lamarck publishes his hypothesis of evolution. Hutton proposes his theory of gradualism. Linnaeus (classification) Cuvier (fossils, extinction) Malthus (population limits) Lamarck (species can change) Hutton (gradual geologic change) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection)

Natural Selection (Darwin) Better adapted organisms are more likely to survive and become parents Population changes over time; frequency of favorable traits increase with each generation

4 observation for Natural Selection 1) Variation – each individual is unique – Some advantageous traits - inherited 2) Overproduction – each species can produce more offspring than can survive 3) Limits on Population Growth – (struggle for existence) more individuals than resources  competition 4) Differential reproductive success – (survival of the fittest) better adapted individuals will survive and reproduce

Fig

Evidence for Evolution Fossil Record Comparative Anatomy Biogeography Developmental biology Molecular evidence

Fossil Record Fossils – remains/traces of previously existing organisms – Sedimentary rock, bogs, tar, amber, ice – Conditions slow or prevent decay – Covered quickly – water, sand – Hard body parts – Record biased – location, body

Dating Fossils 1) Relative Age – position in rock – Index fossils – characterize a specific layer over large geographical areas Existed short time, preserved in large numbers – With this info  arrange rock layers and fossils in chronological order and identify comparable layers in widely separated locations

Fig Younger stratum with more recent fossils Layers of deposited sediment Older stratum with older fossils

2) Absolute Age – – Radioisotopes – emit radiation – nucleus changes into nucleus of different element with decay – Half-life – time required for ½ of the atoms to change to a different atom – Potassisum-40 (1.3 billion years) – Uranium-235 (704 million years) – Carbon-14 (5730 years)

Comparative Anatomy Similar structures  related organisms (common ancestor) Homologous structures – features derived from same structure in a common ancestor – Ex: limb bones of mammals, modified leaves – Similar structure, different function Homoplastic features (Analogous features) – structurally similar features that are not homologous but have similar functions in distantly related organisms – Ex: wings of insects/birds, spines and thorns – Same function, evolved separately (different structure)

Fig Humerus Radius Ulna Carpals Metacarpals Phalanges HumanWhale Cat Bat

Fig Sugar glider Flying squirrel AUSTRALIA NORTH AMERICA

– Show organisms with separate ancestries may adapt in similar ways to similar environmental demands  Convergent evolution Ex: aardvarks, anteaters, pangolins Vestigial structures – organs or parts of organs that are seemingly nonfunctional and degenerate, undersized or lacking some essential part – Remnants of parts that were functional in ancestors – Ex: Human - appendix, coccyx, 3 rd molars, ear muscles Whales/pythons – hind limb bones Pigs – vestigial toes Kiwi – wingless bird – vestigial wing bones Burrowing/cave-dwelling – vestigial eyes Vestige usually not harmful so selective pressure to completely eliminate is weak

Biogeography Study of past and present geographical distribution of organisms Not all animals/plants found in all environments where they could survive Spread from origin Continental drift / Pangaea

Developmental biology Genetic similarities reflect shared evolutionary history Vertebrates – embryological development similar  common ancestor – (segmentation, gill pouches, aortic arches)

Fig Human embryoChick embryo (LM) Pharyngeal pouches Post-anal tail

Molecular evidence Confirms structural and fossil evidence Universal genetic code Similar amino acid sequences, proteins, nucleotides More similarities  common ancestor Phylogenetic trees - diagrams showing lines of descent – Derived from differences in DNA sequences – Whales and hippos closely related

Evolution is happening NOW! Can be observed in our lifetime Ex: – Resistant Bacteria – Finch beaks – Guppy study